[Evolution] how are threads sorted?

[Thomas Emmel <emmel mechanik tu-darmstadt de>]

Hi all,

all the time I am just wondering how the algorithm to build a thread in
evo works...
It works mostly realy fine but sometimes there are curious threads like
(I have to type it, cause I will not add a picture of evo itself ;-)

janne...    - [Evolution] _Very_ strange sizing problem
jeffrey...    - Re: [Evolution] _Very_ strange sizing problem
steven...     | - [Evolution] Launching
peter...      |   |_ Re: [Evolution] Launching
ritchie...    |   |_ Re: [Evolution] Launching
den...        |   |_ Re: [Evolution] Launching
luis...       |_ Re: [Evolution] _Very_ strange sizing problem

and so on.
Why did this happen???

Thomas Emmel